I haven't seen one of those for decades. It is a PricePfister FlowMatic valve, call 1-800-PFAUCET and see if PP still stocks the parts, other than the operating mechanism, otherwise do an Internet search for FlowMatic and maybe you will find one somewhere.

Around here, you can still find that handle and cartridge in some of the local hardware stores....Dixiline, Ace, etc. in certain neighborhoods where developers used a lot of that valve. Not likely to find it in blue or orange. You can find it here : c******************
look at item# 444000 handle, and item # 485750
note: the commercial website I wanted to reference is blocked by the board filters. If you want to search for the items on line, PM me.

A word of advice: although the cartridge still is in a PP OEM package, for MANY years they have been sourcing it from Alsons, who gets it in Mexico. The original ceramic disc cart was quite long lasting. The imports seem to exhibit a lot of infant mortality and catastrophic failures. I would strongly think about getting a new valve installed.